1. Field of the Invention
The invention relates to a mount for an optical element in an optical imaging device, having at least one mounting ring which bears the optical element according to the preamble of claim 1.
2. Description of the Related Art
It is known from DE 198 59 634 A1 and DE 199 04 152 A1, for example, that mounting rings for optical elements, in particular for optical elements for semiconductor lithography, where correspondingly high levels of accuracy are required, are designed such that an inner mount is attached to an outer ring of the mount via elastic elements. These elastic attachments allow precision adjustment of the position of the optical element, together with a certain isolation of the latter from deformation caused by this precision adjustment. The elastic attachment, however, gives rise to a system which can vibrate, very small eigenfrequencies being produced as a result of a correspondingly large mass of the combination of optical element and inner ring. The optical element can thus, disadvantageously, very easily be caused to vibrate.
It is also disadvantageous that, via the elastic attachments, the outer ring can be subjected to deformation which occurs, for example, when the outer ring is mounted on other mounts or when the lens-system structures connected firmly to the outer ring are mounted on the housing of the lens system. This deformation is then transmitted to the inner ring, in part, by the elastic attachments and may result there in undesired deformation of the optical element. The deformation of the inner ring is manifested here predominantly by bending in the radial and axial directions and by torsion in the tangential direction. In order for this deformation, which can then be transmitted from the inner ring to the optical element, to be kept to as low a level as possible, the inner ring may be designed to be very rigid in relation to this deformation. This inevitably results, however, in comparatively large and heavy inner rings, which further worsen the above-mentioned problems in respect of the low eigenfrequencies.
The object of the invention is thus to avoid the above-mentioned disadvantages and to provide a lightweight and stable mounting ring which has a very high level of rigidity in respect of radial and axial bending and torsion in the tangential direction.
This object is achieved according to the invention by a mount, wherein the mounting ring is of at least partially hollow design in cross section.
Using a mounting ring which is of at least partially hollow design in cross section can achieve the situation where, with minimal use of mass, a very high geometrical moment of inertia about the radial and axial axes and a high torsional moment of inertia about the tangential axis are achieved. This construction thus makes it possible, according to the invention, to provide a lightweight and nevertheless stable mounting ring and developments.
A particularly favorable embodiment of the invention here provides that the mounting ring, which bears the optical element, forms an inner ring of the mount, said inner ring being connected to an outer ring of the mount via a plurality of elastic elements.
In the case of such a combination which provides a construction which can vibrate, the abovementioned advantages of the mounting ring according to the invention come into play to very good effect. Since the mounting ring, despite its very high level of rigidity, may be of very lightweight design, there is an increase in the eigenfrequency of the combination of optical element and mount when the mounting ring is attached via elastic elements. Since the mounting ring, at the same time, has the very high level of rigidity, which has already been mentioned a number of times, deformation transmitted to it via the elastic attachments is only transmitted to a minimal extent, if at all, to the optical element.
In a further favorable embodiment of the mount, the mounting ring is designed as a hollow profile with a gap-free border region throughout.
Such a design of the hollow profile allows the highest geometrical moments of inertia with the smallest possible amount of material being used. Since the continuous border region does not have any gap, slit or the like, it is thus also possible to optimize, in addition to the two geometrical moments of inertia in respect to radial and axial bending, the torsional moment of inertia in respect of the mass of material used.
Furthermore, the inventors have found that, in a particularly favorable development of the invention, the mounting ring should have a ratio between its radial width and its axial height of from 0.25 to 1.
Dimensions which have such a ratio of width to height of from 0.25 to 1 make it possible to achieve the highest geometrical moments of inertia for the design of the mounting ring. It is more or less immaterial here as to whether the cross section is rectangular or round in shape.
Further advantageous configurations of the invention can be gathered from the rest of the subclaims and from the exemplary embodiments illustrated hereinbelow with reference to the drawing, in which: